What Is a Network Switch? Functions, Types, and Configuration Explained

1. Concept of a Switch

A switch (meaning "switch") is a network device used for forwarding electrical (or optical) signals, providing a dedicated communication path between any two connected nodes. The most common type is an Ethernet switch, but there are also telephone voice switches and fiber optic switches.

Example: In a dormitory with a single broadband line shared by six users, a switch can provide multiple ports to create a star topology, allowing each user to have an independent connection.

Note: Ethernet cables carry electrical signals, while fiber optic cables carry light signals. Switches may have RJ45 ports and SC fiber ports, enabling PC communication within a LAN.

2. Working Process

When a port is successfully connected, the switch creates a MAC address table by mapping MAC addresses to ports. Later, when sending or receiving data, packets destined for a known MAC address are forwarded only through the corresponding port.

Explanation: After a device connects, its physical (MAC) address is associated with the port and stored in the MAC table. The switch uses this table to forward packets based on the MAC address.

3. Switch Functions

Learning

The switch learns MAC addresses and stores them in an internal address table, establishing temporary switching paths between source and destination frames.

Forwarding/Filtering

Based on the MAC address, the switch forwards the packet to the appropriate port (forwarding) or does not send it to other ports (filtering). If the destination MAC is in the table, the frame is sent only to the associated port; broadcast/multicast frames go to all ports.

Loop Elimination

When a redundant loop exists, Ethernet switches use the Spanning Tree Protocol to prevent loops while allowing backup paths.

Switching Modes

Switching mode refers to how a switch forwards data from one port to another. The main modes are:

Store and Forward : The switch stores the entire frame, performs CRC error checking, and forwards it if error‑free. Advantages: no corrupted frames are forwarded. Disadvantages: slower than cut‑through.

Cut‑Through : The switch reads the first 6 bytes to determine the destination MAC and begins forwarding immediately, resulting in lower latency. Advantages: fast forwarding and higher throughput. Disadvantages: may forward corrupted frames.

Fragment‑Free : Checks that the frame is at least 64 bytes long; frames shorter than 64 bytes are discarded. Faster than store‑and‑forward but slower than cut‑through.

4. Classification of Switches

Switches can be classified by:

Network scope: LAN switches vs. WAN switches.

Transmission medium and speed: Ethernet, Fast Ethernet, Gigabit Ethernet, 10‑Gigabit Ethernet, ATM, FDDI, Token Ring.

Network layer: Enterprise, campus, departmental, workgroup, desktop switches.

Port structure: Fixed‑port vs. modular switches.

Protocol layer: Layer‑2, Layer‑3, Layer‑4 switches.

Management capability: Managed vs. unmanaged switches.

Broadly, switches are divided into non‑managed, lightly managed, and fully managed types.

Non‑Managed Switch

Provides multiple ports for plug‑and‑play use, suitable for simple monitoring or aggregation networks.

Lightly Managed Switch

Supports iVMS‑4200 client management, topology management, QoS, and port management. It can be managed via a mobile app for status monitoring, topology view, and port reboot.

Fully Managed Switch

Offers both web and command‑line management, providing comprehensive configuration options.

5. Why a 100 Mbps Switch Doesn’t Deliver 100 MB/s Download Speed

Switch speed is expressed in Mbps (megabits per second). Since 1 Byte = 8 bits, 100 Mbps equals 12.8 MB/s. Therefore, a “100 Mbps” switch can at most provide about 12.8 MB/s download speed.

6. Switch Layers and Selection

Switches are often categorized into access, aggregation, and core layers in a three‑tier network architecture:

Access Layer

Connects end devices, provides low‑cost high‑port‑density ports, and may include basic user management features.

Aggregation Layer

Aggregates traffic from multiple access switches, provides higher performance, and may implement VLAN routing and filtering.

Core Layer

Serves as the backbone, requiring high reliability, high throughput, and low latency. Core switches are typically gigabit or 10‑gigabit capable.

7. Switch Types by Interface

RJ‑45 (copper twisted‑pair) – most common, used for 10/100/1000 Mbps Ethernet.

Fiber optic interfaces – used for 100Base‑FX, 1000Base‑FX, etc.

AUI – 15‑pin connector for coarse‑coaxial cable (rare today).

BNC – 10‑base‑2 thin‑coaxial connector (rare).

Console – for configuration (RJ‑45 or serial).

FDDI – fiber‑distributed data interface (legacy).

8. Connection Methods

Cascading

Connecting switches via regular ports (using crossover cables) or uplink ports (using straight‑through cables). Modern switches often auto‑detect cable type.

Redundancy (Spanning‑Tree)

One link is active while others are in standby, improving reliability.

Stacking

Multiple switches are combined to act as a single logical switch, increasing port density and bandwidth. True stacking uses dedicated stacking modules and cables; virtual stacking uses regular Ethernet ports.

9. Switch Working Characteristics

Switches have a high‑bandwidth backplane and internal switching matrix. Incoming frames are examined, the destination MAC is looked up in the MAC table, and the frame is forwarded to the correct port. If the MAC is unknown, the frame is flooded. The switch then learns the source MAC address.

10. Switch Features Compared to Bridges and Hubs

Parallel communication increases throughput.

Segmentation into multiple collision domains reduces congestion.

Support for VLANs adds flexibility.

High port density comparable to hubs.

11. Laboratory Steps (Cisco‑style Configuration)

Switch> enable</code>
<code>Switch# conf terminal</code>
<code>Enter configuration commands, one per line. End with CNTL/Z.</code>
<code>Switch(config)# hostname S1</code>
<code>S1(config)# enable secret cisco</code>
<code>S1(config)# line vty 0 15</code>
<code>S1(config-line)# password cisco</code>
<code>S1(config-line)# login</code>
<code>S1(config)# interface f0/1</code>
<code>switch(config-if)# duplex { full | half | auto }</code>
<code>switch(config-if)# speed { 10 | 100 | 1000 | auto }</code>
<code>S1(config)# int vlan 1</code>
<code>S1(config-if)# ip address 172.16.0.1 255.255.0.0</code>
<code>S1(config-if)# no shutdown</code>
<code>S1(config)# ip default-gateway 172.16.0.254</code>
<code>S1# copy running-config startup-config</code>
<code>Destination filename [startup-config]?</code>
<code>Building configuration...

12. POE Switches vs. Ordinary Switches

Traditional switches only transmit data. POE switches can also deliver power over Ethernet, reducing the need for separate power cables and providing safety features such as short‑circuit, overload, and surge protection. POE switches detect POE‑capable devices and only supply power when appropriate.

13. POE Power Calculation (Example: Hikvision DS‑3E0326P‑E)

Parameters include the number of 802.3at and 802.3af devices, per‑port power limits (≤25.5 W), and total power budget. The switch’s spec table shows the maximum POE power per port and overall.

14. What Is Switching Capacity?

Switching capacity (or fabric capacity) is the total bandwidth the backplane can handle, often expressed in Gbps or Tbps.

15. What Is Packet Forwarding Rate?

Packet forwarding rate measures how many packets per second the switch can process.

16. Switch Form Factors

Switches come in box (stand‑alone) and chassis (rack‑mount) forms. Box switches are compact, while chassis switches offer modularity and higher port density.

17. Switch Architecture Evolution (Chassis)

Shared bus – simple but limited bandwidth.

Ring – bus moved onto a chip, modest improvement.

Shared memory – uses large RAM and a central engine; scalability limited.

Crossbar + shared memory – combines crosspoint matrix with memory for higher performance.

Distributed Crossbar (CLOS) – multi‑stage architecture separating control and data planes for high capacity and reliability.

18. Chassis Components

Key modules include the backplane, control board (management and control plane), switching fabric board (data plane), and line cards (interface boards). The backplane connects all modules; the control board handles protocols and device monitoring; the fabric board performs high‑speed packet switching; line cards provide physical ports.

19. Rack‑Mount Switches

Rack‑mount switches are modular, fit standard 19‑inch racks, and support various network types. Stacking switches can be mounted in racks or used as standalone units.

20. Common Switch Brands

Department‑level switches: TP‑Link (普联). Enterprise‑level switches: Huawei, H3C, Ruijie, Cisco (Huawei dominates Chinese market). Education sector often uses Ruijie; Cisco usage is decreasing in China.

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